(1) Field of the Invention
This invention relates to indirect extrusion presses, and more particularly to an indirect extrusion press which employs a combination of a loose die and a cleaning mechanism for scraping off shells from inner surfaces of a container during extrusion of a material through the die and which permits repeated use of one and same die in the successive extruding cycles by cooperative operations of a die handling mechanism and a discard billet shearing mechanism.
(2) Description of the Prior Art
There is illustrated in FIG. 1 a typical example of the conventional indirect extrusion press, which has a die 2 assembly consisting of a die and a die holder detachably mounted on a die stem 1 and moved relative to and in a billet receptacle bore 4 of a container 3 loaded with a billet A, thereby extruding a product 5 of a predetermined shape. Upon completion of an extruding cycle, a discard billet stub 6 which remains at the tail end of the extrudate 5 at the fore end of the container 3 is cut off by a discard shear mechanism 7.
FIGS. 1(a) to 1(h) show the successive phases of the extruding operation by the conventional indirect extrusion press. In the initial stage of the operation, a billet A and a die assembly 2 are inserted side-by-side into the billet receptacle bore 4 of the container 3 as shown at (a) and (b) shown in FIG. 1. In the next phase of FIG. 1(c), the billet A is sandwiched between a dummy block 8 and the die assembly 2 in axial alignment therewith, and a mandrel 10, mounted in a pressing stem 9, protrudes into the billet A until the mandrel tip opposingly faces the die hole of the die assembly 2 in small gap relation therewith to complete piercing of the billet A. Then, as shown at (d) and (e) of FIG. 1, the billet A is extruded into a tubular form 5 through the die hole, sending forward the extruded product through die stem bore 11 of the die stem 1. Upon completion of the extrusion, the die assembly 2 is supported by an intermediate frame 12 as shown at (f) of FIG. 1, and the discard billet stub 6 and dummy block 8 are gripped by a chuck mechanism 13. In synchronism with the shearing action of the discard shear mechanism 7 against the discard billet 6, the chuck mechanism 13 is retracted to remove the billet stub 6 from the extrudate 5. Thereafter, the extrudate 5 is drawn out of the press machine of the die assembly 2 is transferred to a position outside the machine, while the container 3 and pressing stem 9 are returned to the respective initial positions as shown at (g) and (h) of FIG. 1.
In the indirect metal extrusion, especially in the extrusion of a high tensile aluminum alloy, it is necessary to remove shells which deposit on the inner surfaces of the container, for ensuring a satisfactory surface quality of the extrudate. This has heretofore been accomplished by backstroking through the container a dummy block or a die which is provided with a cleaning edge around the circumference thereof or which has a cleaning disc attached thereto, subsequent to the billet extruding phase. In this connection, it has also been known to use a loose die with a cleaning flange around its rear edge to complete the shell removal simultaneously with the billet extrusion. In any case, a problem is encountered either in that the time of each cycle of press operation is prolonged by the shell-removing operation or in that a number of dies or die assemblies have to be provided due to difficulty of cleaning a used die or die assembly during a dry cycle of the press operation. Therefore, it has been required to provide complicated and costly equipment for cleaning and circulating a number of dies one after another in relation with the cycle of the press operation. The use of a number of dies gives rise to another problem that a very severe tolerance has to be observed in the fabrication process of the die assemblies to ensure dimensional uniformity of extruded products.
A further problem which is encountered in the indirect extrusion by the conventional press is that the discard billet stub is subject to deformation in the shearing stage, making it difficult to grip it securely by the chuck mechanism 13. In this connection, FIGS. 2 and 3 show another conventional indirect extrusion press, in which a discard billet stub is cut off from an extrudate by exposing the discard stub 6 from a container 3 with a die assembly 2 still in a billet receptacle bore 4 of a container 3 as shown particularly in FIG. 3. This sort of extrusion press also involves the problem that billet receptacle bore 4 is susceptible to deformations or other damage by the great load which is imposed on the container in the discard shearing stage.